The present invention relates generally to column grid arrays for semiconductor packaging and more particularly, to an apparatus for aligning and dispensing a plurality of solder columns in an array. After alignment, the solder columns are positioned in an array of corresponding electrically conductive contact pads or terminals disposed on one side of a ceramic substrate. The solder columns are reflowed in an oven and then, attached to the substrate to form a ceramic column grid array package.
As the density of electronic devices on integrated circuits has continued to increase, the number of leads required for a chip has also increased. To handle the increased density, there has been developed a ball grid array package wherein one or more chips are mounted on the top surface of a substrate. The ball grid array package uses an array of solder balls to provide electrical connections between the substrate and a printed circuit board. A problem with this type of package is that substantial differences in the thermal coefficient of expansion can exit between the substrate and the printed circuit board. Such differences in the thermal coefficient of expansion cause plastic deformation of the solder balls.
This problem has been addressed by the use of a ceramic column grid array package. The column grid array package uses an array of solder columns, rather than solder balls, to make electrical connections between a ceramic substrate and a printed circuit board. The solder columns typically have a height of approximately 2.55 mm and a diameter of 0.50 mm. The taller configuration of the solder columns offers compliancy to better absorb the differential thermal expansion rate between the ceramic column grid array package and the printed circuit board. To attach the solder columns to the semiconductor substrate, a low melting temperature solder paste is deposited on electrically conductive contact pads which are, in turn, placed on one side of the ceramic substrate. The solder columns, typically made from a high melting temperature solder using a nominal 90/10 alloy of lead to tin, are vertically positioned on the corresponding contact pads. The combination is then heated in a reflow oven so that the solder paste is reflowed to make a connection between the solder columns and the pads. Like procedure takes place when the solder columns are attached to the printed circuit board.
In the manufacture of a ball grid array package, a vacuum pickup tool is typically used to pick up and place a multiplicity of solder balls in the desired pattern on a semiconductor substrate. The spherical shape of the solder balls makes it easier to pick up and place a full array of solder balls on the substrate. On the other hand, solder columns have a cylindrical shape and must, therefore, be arranged in a fixed orientation during pickup. No means has heretofore been proposed to align a multiplicity of solder columns in an array before the solder columns are picked up.
Accordingly, it is an object of the present invention to provide an apparatus for aligning and dispensing a plurality of solder columns in an array, so that all the solder columns can readily be picked up by a vacuum pickup tool.